1. Field of the Invention
The present invention relates to a gas-barrier film, in particular to a laminate-type gas-barrier film favorable for a substrate for various devices and for a coating film for devices, and to an organic electroluminescent device (hereinafter referred to as “organic EL device”) that comprises the above gas-barrier film and has good durability and flexibility.
2. Description of the Related Art
Heretofore, a gas-barrier film fabricated by forming a thin metal oxide film of aluminium oxide, magnesium oxide or silicon oxide on the surface of a plastic substrate or a film is widely used for wrapping or packaging articles that require shielding from various gases such as water vapor or oxygen and for wrapping or packaging edibles, industrial articles and medicines for preventing them from being deteriorated. Apart from its applications for wrapping and packaging articles, in addition, the gas-barrier film is being used for substrates for liquid-crystal display devices, solar cells and EL devices. In particular, a transparent substrate that is being much used for liquid-crystal display devices and EL devices is required to be lightweight and has a large panel and, in addition, it is further required to satisfy high-level performance ability in that it has long-term reliability and has a lot of latitude in designing its shape and that it enables curved-face display.
Recently, in the field of liquid-crystal display devices and EL devices, a film substrate of transparent plastics or the like is being used in place of a glass substrate that is heavy and readily cracked or broken and hardly worked into a large-size panel. In addition, since the film substrate of transparent plastics or the like satisfies the above-mentioned requirements and since it is applicable to a roll-to-roll system, it is more advantageous than glass in that the producibility with it is high and the production cost with it is low. However, the film substrate of transparent plastics or the like is problematic in that its gas-barrier property is not good as compared with that of glass. When a substrate having a poor gas-barrier property is used, water vapor and air may penetrate through it; and, for example, when it is used in liquid-crystal display devices, the liquid crystal in the liquid-crystal cell may be degraded and the degraded part may be a display failure, thereby worsening the display quality of the devices.
For solving the problem, it is known to form a thin metal oxide film on the above-mentioned film substrate, thereby using the resulting gas-barrier film as a transparent substrate. As a gas-barrier film for use in wrapping materials and liquid-crystal display devices, there are known a plastic film coated with silicon oxide through vapor deposition (for example, see JP-B-53-12953, pp. 1-3), and a plastic film coated with aluminium oxide through vapor deposition (for example, see JP-A-58-217344, pp. 1-4). These have a water-vapor barrier level of 1 g/m2·day or so. However, with recent development of large-panel liquid-crystal display devices and high-definition display devices, the film substrate is being required to have a water-vapor barrier level of 0.1 g/m2·day or so.
Extremely recently, the development of organic EL devices and high-definition color liquid-crystal display devices that are required to have a higher gas-barrier level is being further promoted, and a substrate that keeps a transparency applicable to them and has a higher gas-barrier level, especially a higher water-vapor barrier level of not more than 0.1 g/m2·day is being required.
To satisfy these requirements, some methods expected to produce a higher gas-barrier level have been investigated, for example, a sputtering method of forming a thin film by the use of a plasma generated through glow discharge under low pressure, and a CVD method for film formation. In addition, an attempt to change laminate structure formation to attain a desired result is tried (for example, see JP-A-2003-206361, pp. 2-3).
However, when a film substrate is used, the substrate temperature is limited in layer formation thereon, and therefore a barrier layer having a sufficiently dense and tight structure could not be formed, and a film having a satisfactory barrier property capable of satisfying the requirements could not as yet be formed.
As a thin-film material having a good barrier property, a silicon nitride and a silicon oxinitride are used, and laminating them is tried. For example, U.S. Pat. No. 6,413,645B1 (p. 4 [2-54] to p. 8 [8-22]) describes a barrier film fabricated by laminating, on a substrate film, two layers of a silicon oxinitride having a different nitrogen/oxygen constitution ratio. However, the constitution could not satisfy both a sufficient gas-barrier level and a bending resistance which the film substrate must have in its use, and further technical improvement on it is desired.
On the other hand, a technique of producing a barrier film having an alternate laminate structure of an organic layer/inorganic layer according to a vacuum evaporation method is proposed (for example, see Affinito et al., Thin Solid Films, 1996, P. 290-291 (pp. 63-67)), and it gives a barrier film necessary for a film substrate for organic EL devices.
However, the adhesiveness between the organic layer and the inorganic layer is not always satisfactory, and a multi-layered structure of at least 6 layers is needed for providing a high-reliability barrier film for organic EL devices. To that effect, it is difficult to satisfy both the good performance and the high throughput, and development of a novel film-forming system suitable to a continuous film-forming process is desired.